The present invention relates to a polishing apparatus for polishing a substrate, such as a semiconductor wafer. Specifically, the present invention relates to a polishing apparatus including a novel dresser device. The dresser device is used for regeneration (dressing or conditioning) of a polishing surface of a polishing pad or a polishing plate comprising abrasive particles.
A conventional polishing apparatus of the above-mentioned type is shown in FIG. 1. In FIG. 1, the polishing apparatus comprises a turntable 1 having a polishing pad 2 covering an upper surface thereof and a substrate holder 3 for holding a substrate (not shown) to be polished, such as a semiconductor wafer. A substrate is held on a lower side of the substrate holder 3 and is pressed against a polishing surface of the polishing pad 2 on the turntable 1. While pressing the substrate against the polishing surface, an abrasive liquid is supplied onto the polishing surface, and relative movement between the polishing pad 2 and the substrate is conducted by rotating the turntable 1 in a direction indicated by an arrow A and rotating the substrate holder 3 in a direction indicated by an arrow B. Thus, the substrate is polished to a flat and mirror-finished surface. It should be noted that a polishing plate comprising abrasive particles may be used, instead of the polishing pad 2.
In this apparatus, the polishing surface of the polishing pad 2 becomes clogged after polishing of a plurality of substrates, to thereby lower an efficiency of polishing. Therefore, when a predetermined number of substrates have been polished or the efficiency of polishing has been lowered due to clogging, the polishing surface is scraped for dressing, by means of a dresser 4.
The dresser 4 comprises a dresser tool 5 and a dresser shaft 6 for supporting the dresser tool 5. The dresser shaft 6 is adapted to be rotated by means of a rotary mechanism (not shown) in a direction indicated by an arrow C. The dresser tool 5 is adapted to be pressed against the polishing pad 2 by means of an air cylinder 7 and the dresser shaft 6. An annular projection 5a is formed on a lower surface of the dresser tool 5. The annular projection 5a is formed from a member (such as a diamond pellet) containing diamond particles or a hard material such as a ceramic material. A relative movement between the dresser tool 5 and the polishing pad 2 is conducted by rotating the dresser shaft 6 and the turntable 1, to thereby scrape the polishing surface of the polishing pad 2 for dressing.
For effecting dressing of the polishing surface of the polishing pad 2, air is supplied through the controller 8 to the air cylinder 7, so as to press the dresser tool 5 against the polishing pad 2 under a predetermined pressure. Therefore, the minimum pressure applied to the polishing pad 2 (the pressure when no air is supplied through the controller 8 to the air cylinder 7) is equal to the total of the weight of the dresser tool 5 and the weight of the dresser shaft 6.
During dressing, as shown in FIG. 2, the rate (mm/hr) of scraping of the polishing pad 2 is proportional to the pressure applied to the polishing pad 2. Generally, the total of the weight of the dresser tool 5 and the weight of the dresser shaft 6 is about 10 kg, so that it is impossible to reduce the pressure applied to the polishing pad to less than 100 N (Newton). Therefore, the polishing pad 2 is scraped at a high rate, leading to a rapid wear of the polishing pad 2.
In view of the above, the present invention has been made. It is an object of the present invention to provide a polishing apparatus for polishing a substrate comprising
a turntable having a polishing surface, a substrate holder for holding a substrate and bringing the substrate into contact under a pressure with the polishing surface to polish the substrate, a dresser including a dresser tool adapted to be brought into contact under pressure with the polishing surface to dress or condition the polishing surface and a pressure device connected to the dresser tool for moving the dresser between a raised position where the dresser is spaced away from the polishing surface and a dressing position where the dresser rests on the polishing surface such that the dresser tool is in contact with the polishing surface under a pressure exerted by the weight of the dresser itself. The pressure device includes a member for applying an upward force to the dresser to decrease the pressure and a downward force to the dresser to increase the pressure.
By this arrangement, the pressure between the dresser tool and the polishing surface of the turntable can be adjusted to a level less than that generated by the weight of the dresser itself. Therefore, dressing of the polishing surface can be conducted while suppressing a rapid wear of the polishing surface.
The dresser may comprise a dresser shaft connected to the dresser tool and extending upward vertically from the dresser tool and the pressure device may comprise a cylinder equipped with a piston to which the dresser shaft is connected. A kinetic frictional resistance against movement of the piston in the cylinder is preferably 0.5 kg or less. First and second pressure supply devices may be fluidly connected to the cylinder so that the first pressure supply device supplies a pressurized fluid to the cylinder to apply an upward force to the piston and the second pressure supply device supplies a pressurized fluid to the cylinder to apply a downward force to the piston.
By preliminarily supplying a pressurized fluid to the above-mentioned cylinder so as to counter the weight of the dresser, the pressure between the dresser tool and the polishing surface of the turntable can be easily minimized to a level less than the weight of the dresser and adjusted to an arbitrary value exceeding that level (for example, a value in a range of 10 N to 300 N).
In accordance with another aspect of the present invention, there is provided a polishing apparatus comprising a turntable having a polishing surface, a substrate holder for holding a substrate and bringing the substrate into contact under pressure with the polishing surface, a dresser tool adapted to be brought into contact under pressure with the polishing surface to dress or condition the polishing surface, and a dresser tool holding device for holding the dresser tool and moving the dresser tool between a raised position where the dresser tool is spaced away from the polishing surface and a dressing position where the dresser tool rests on the polishing surface with a pressure being exerted by the dresser tool on the polishing surface by the weight of the dresser tool itself.
By this arrangement, there is no possibility that a pressure exceeding the weight of the dresser tool will be applied to the polishing surface. Therefore, dressing of the polishing surface can be conducted while suppressing a rapid wear of the polishing pad or plate.
The dresser tool holding device may support the dresser tool in such a manner that the dresser tool is substantially freely movable in a vertical direction relative to the dresser tool holding device.
The dresser tool holding device may comprise an air cylinder equipped with a piston connected to the dresser tool to move the dresser tool between the raised position and the dressing position, and there may be provided a shaft extending vertically and having a lower end connected to the dresser tool and an upper end connected to the piston. The dresser tool may be freely movable in a vertical direction relative to the lower end of the shaft. The shaft may be provided at its lower end with a flange extending radially outwardly from the lower end and having vertical through holes formed therein and the dresser tool may be provides with a plurality of vertical connecting pins extending through the through holes of the flange. Each of the connecting pins may be provided with a head adapted to be engaged with an upper surface of the flange when the dresser tool is positioned at the raised position. There may be provided an automatic aligning roller bearing connected between the flange and the dresser tool so that the dresser tool can tilt in compliance with undulations on the polishing surface.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.